Coffee and health

Researchers have for a long time been investigating the impact on health of drinking coffee, and their findings make headlines in part because they give the media what they love; conflict and controversy! My aim here is to clear up some common misconceptions about the subject.

Heart health

The results of research [Superko: AHA poster presentation, 2005] into the hypothesis that decaffeinated coffee may be harmful to the heart suggested that it can raise blood levels of non-esterified fatty acids in the blood, but it is necessary to assess the force of the findings in the context of other research in this area. The study was small, and while its findings may highlight a direction for further research they directly contradict those published in a peer reviewed study on the effects of decaffeinated coffee on serum lipid profiles in healthy young adults (Wahrburg et al, European Journal of Clinical Nutrition, Volume 48, 1994). In this study, consumption of decaffeinated coffee did not lead to any significant changes in serum total and LDL cholesterol, triglycerides or apolipoprotein B.

Grubben et al (2000) asked study participants to drink six large cups of unfiltered coffee a day for two weeks and compared them to those drinking filtered coffee. The unfiltered coffee group showed an increase in serum LDL cholesterol of 2mg/dl. After two weeks, this group switched to filtered coffee and their serum cholesterol returned to baseline. Christensen et al (2002) have found that volunteers (who had been drinking on average 4 cups of filtered caffeinated coffee daily for the past year) who abstained completely from coffee for 6 weeks showed a drop of 0.2 mmol/L in their total cholesterol concentration. However, interesting though these results are, they don’t tell us anything about the long term effects of habitual moderate coffee intake.

Coffee has many ingredients that may contribute to its biological activity, for example heterocyclic compounds, which exhibit strong antioxidant activity. Good antioxidant status is crucial for the prevention of the oxidation of cholesterol, and the onset of atherosclerosis, so it is possible that the positives ? contributing to antioxidant intake – outweigh a small rise in blood cholesterol levels? It appears so far that that drinking moderate amounts of filtered coffee comes with no risk of adverse cardiovascular effects. In fact the data show that coffee has a significant antioxidant effect, and may have an inverse association with the risk of heart disease and of type 2 diabetes mellitus.

It is true that epidemiological studies suggest that consumption of boiled coffee (a variety prepared in Scandanavia and the Middle East) is associated with a greater risk of cardiovascular disease. However, the effect is caused by cafestol and kahweol – the two diterpenes in the lipid fraction of coffee grounds – which are believed to be responsible for increase concentration of cholesterol in plasma. They are only present at low levels in filtered and instant coffee.

Blood pressure

The recently published Nurse?s Health Study (Winkelmayer et al. 2005), the largest study to date to have looked at a possible association between coffee and health, concludes that there is no association between regular moderate coffee consumption and an increased risk of developing hypertension. However, epidemiological studies suggest that through regular consumption, some people develop tolerance to cardiovascular responses to coffee, and so show no systematic elevation of blood pressure in the long-term.

Conception and childbirth

There is evidence to suggest that high coffee consumption is associated with infertility, increased risk of miscarriage, and low birth weight. Bech et al. (2005) found that women who drink 8 or more cups of coffee a day are at 75 per cent more risk than average of miscarriage or stillbirth, and that those who drink between a third of a cup and 3 cups daily increase their risk by 3 per cent.

The Food Standards Agency (FSA) recommends that pregnant women consume no more than 300mg of caffeine per day, which in terms of coffee means 4 cups, or 3 mugs, of instant, or 3 cups of filtered. It is the equivalent, also, of about six cups of tea.

Dr Sarah Schenker is a qualified state registered dietician and member of the British Dietetic Association and the Nutrition Society. She works part-time as a nutrition scientist for the British Nutrition Foundation and is a consultant sports dietician for Delia Smith and Norwich City Football Club.